The Patient Protection and Affordable Care Act eliminated cost sharing for preventive services, including colorectal cancer screening for individuals aged 50-75 years with private health insurance. This study examines the impact of the Affordable Care Act’s removal of cost sharing for colorectal cancer screening on colorectal cancer incidence and mortality. Trends in colorectal cancer incidence and colorectal cancer‒related mortality were modeled among 2,113,283 Kaiser Permanente Northern California members aged ≥50 years between 2003 and 2016 using an interrupted time-series design. As a sensitivity analysis, a controlled analysis utilized a comparison group of members covered with pre‒Affordable Care Act zero cost sharing for colorectal cancer screening. Analyses were performed in 2019 and 2020. The colorectal cancer incidence dropped by 17% around the time the Affordable Care Act was enacted (change in level incidence rate ratio; 95% CI=0.77, 0.90, 2-sided p-value <0.0001), followed by a 3% further decrease per year (95% CI=0.93, 1.00, p=0.05). A similar pattern was observed for colorectal cancer‒related mortality. The controlled results indicated that the elimination of cost sharing for screening due to the Affordable Care Act was associated with greater improvements in colorectal cancer outcomes among members previously covered by health plans with out-of-pocket costs for screening than among those with health plans with zero cost sharing for screening before the Affordable Care Act. The elimination of cost sharing for colorectal cancer screening due to the Affordable Care Act was associated with a decrease in age-, race/ethnicity-, and sex-adjusted colorectal cancer incidence and colorectal cancer‒related mortality, implying that policies that remove barriers to screening, particularly financial burden from cost sharing, can result in improved colorectal cancer outcomes.